It is well known that improved air-fuel mixing provides advantages in reduced knock, improved emission characteristics and improved combustion efficiency in internal combustion (“IC”) engines. In addition to improving the completeness of the fuel combustion, improvements in mixing of the fuel and air allow the engine designer to utilize greater engine compression ratios without producing engine “knock” and, therefore, may further improve engine efficiency.
Improved air-fuel mixing in an IC engine may be achieved by providing a suitable geometry in the combustion chamber, defined generally by the piston and cylinder head, such that during the compression stroke the piston will generate a transverse fluid motion and thereby generate additional turbulence in the combustion chamber. For example, it is known to use a so-called “squish jet” geometry, wherein the piston head and corresponding cylinder head are designed such that one or more peripheral portions of the piston head extend upwardly to substantially fill a corresponding portion of the combustion chamber volume when the piston is near the top of the compression stroke, while recessed portions of the piston head define the actual combustion volume. As the peripheral piston head portion approaches the cylinder head, the air or air-fuel mixture therebetween is pushed out, producing a generally transverse fluid flow in the combustion chamber that increases turbulence and enhances air-fuel mixing.
A prior art example disclosing the use of squish jets to increase turbulence of the air-fuel mixture is U.S. Pat. No. 5,103,784 (hereby incorporated by reference, in its entirety), which discloses a combustion chamber wherein the piston and/or cylinder head have a compression face that defines a bowl portion, and a plurality of squish jet channels arranged about the bowl portion. The channels provide a flow path directing the compressed air-fuel mixture toward the bowl portion. U.S. Pat. No. 6,199,544 (hereby incorporated by reference, in its entirety) discloses a similar apparatus wherein angled squish areas impel the air-fuel mixture toward the center of the combustion chamber. See also, U.S. Pat. No. 6,237,579 and U.S. Pat. No. 6,708,666 (hereby incorporated by reference, in their entirety).
However, prior art squish jet designs do not provide optimal mixing between the air and fuel, and therefore additional improvements in such mixing remain a desirable goal.